The need in mining technology for optimal planing of the mining of an underground deposit and the need to provide for the safety of the personnel involved, combined with the desire for increased mining productivity, require more and more detailed information concerning the geologic-tectonic structure of the underground deposit itself as well as knowledge of the exact limits of the deposit.
Geological mapping provides compositional and tectonic information concerning regions actually explored. However, it is very often necessary to extrapolate from the information concerning the actually explored region, in order to develop a picture of the structure and/or composition of the adjoining unexplored regions. Effective geophysical methods which can be used underground to achieve the aforementioned goal are very much needed.
It is known to detect a compositional discontinuity in a large tectonic structure through the utilization of elastic waves, produced by explosion, hammer blows or vibration, when the elastic parameters of the geological material located on the two sides of the discontinuity are sufficiently different from each other.
These seismic exploration methods have also been used experimentally in underground applications, but in such applications they are not characterized by the same versatility, adaptability and convenience, because the requisite preparatory work and the cost and complexity of performing the requisite measurements and evaluations are far too great.
It has also been realized that different petrologically defined rock formations have different electrical parameters, and this realization has lead to a number of geoelectrical exploration methods.
None of the prior-art methods has passed beyond the status of a laboratory technique and found any wide use in the mining industry itself. The prior-art techniques involve either pure drilled bore methods performed on an electromagnetic basis aboveground and capable of detecting only individual discontinuity locations--namely individual discontinuity locations at the boundaries of the underground deposit--or else involve methods for use in the case of bed-like deposits according to which shallow drilled bores serve to support or accommodate antennas for the detection of the level of irregular bodies intermediate the bed-like deposit and the ground surface; or else involve methods which can be performed aboveground without the use of drilled holes but which aim only for information concerning the structure of shallow deposits.
In summary, the general trend of development in the prior art has been towards the solution of special-case-type problems, the detection of particular kinds of tectonic situations, and the answering of specific questions concerning a geological structure, and not towards the determination of the composition and geometry of underground deposits pretty much irrespective of their size, shape, composition and location relative to the ground surface.
The prior-art methods cannot be employed in the case of underground salt deposits. This is because the particular prior-art method involved can only lead to the answering of one or another single question concerning the composition or structure or geometry or subsurface location, and/or because the prior-art methods involve the use of complicated equipment which is difficult to move from one location to another and which, even just for reasons of space, preclude their use at any arbitrarily selected measuring location.
The known methods, for economic reasons, have found no practical application, because they necessitate very expensive preparatory and auxiliary work, such as the drilling of deep holes or holes in the actual body of the deposit, and because they are time-consuming and expensive, insofar as the use of personnel for performing measurements and evaluations is concerned.
Methods involving the drilling of holes can be used in the case of salt deposits only to a limited extent, since they cannot be employed where the region of the deposit is threatened by water and/or gas.